1. Field of the Invention
The present invention relates to headbox jet velocity measurement for optimizing jet to wire velocities.
2. Description of the Prior Art
In U.S. Pat. No. 3,464,887, S. M. Salomon discloses a sensing device which is constructed to be inserted into and withdrawn from a slice delivery strain. A similar type of structure is provided by Solomon in U.S. Pat. No. 3,509,022.
In U.S. Pat. No. 3,562,105, D. B. R. Hill discloses a slice jet measuring apparatus in which a hollow tube element is disposed in a headbox jet to transmit pressure to a pressure measuring gauge or the like.
J. F. Schmaeng, in U.S. Pat. No. 3,399,565, discloses apparatus in which an impact tube may be moved into a stock flow at a slice opening and the static pressure of the fluid in the tube provides an indication of the velocity of stock flow.
All of the patents discussed above require some sort of physical contact with the headbox jet.
In U.S. Pat. No. 3,337,393, J. D. Parker discloses a headbox jet velocity indicator which includes the use of pressure taps upstream of the slice.
In U.S. Pat. No. 3,487,686, Solomon discloses the use of a pair of pressure transducers in the slice delivery area for measuring the time differential between two signals from the headbox jet.
S. Bauduin et al in their article "A Paper Sheet Contactless Linear Speed Measurement", IFAC PRP Automation, Vol. 4, 1980, disclose a technique for measuring linear speed without contact in which speed measurement by correlation of two optical signals is provided using a single signal laser transducer.
The article "An Optical Correlation Flowmeter for Pulp Stock", by Daniel M. Shellhammer, published in the periodical Tappi, May 1975, Vol. 58, No. 5, pp. 113-116, discusses an optical correlation flowmeter for measuring the flow of water or the like through a pipe. A similar device is disclosed in the Eur-Control Optical Flow Transmitter brochure B2l8.80a, available from Eur-Control U.S.A. Inc., 2579 Park Central Blvd., Decatur, Ga. 30035.
A. A. Rocheleau in U.S. Pat. No. 3,620,914 discloses a scanning system which is employed to measure velocity on the basis of a Doppler frequency shift. In order to measure Doppler shift, a coherent, monochromatic source is required, e.g. a laser. The disadvantage of this type of system is that the laser must be quite powerful in order to obtain a strong signal and could create a hazardous situation to operating personnel.